This invention relates to endovascular graft systems for the repair of aneurysms. In particular, this invention relates to an endovascular graft system for use in repairing abdominal aortic aneurysms.
Aortic aneurysms represent a significant medical problem for the general population. Aneurysms within the aorta presently affect between two and seven percent of the general population and the rate of incidence appears to be increasing. This form of vascular disease is characterized by a degradation in the arterial wall in which the wall weakens and balloons outward by thinning. If untreated, the aneurysm can rupture resulting in death within a short time.
The traditional treatment for patients with an abdominal aortic aneurysm is surgical repair. This is an extensive operation involving transperitoneal or retroperitoneal dissection of the aorta and replacement of the aneurysm with an artificial artery known as a prosthetic graft. This procedure requires exposure of the aorta through an abdominal incision extending from the lower border from the breast bone down to the pubic bone. The aorta is clamped both above and below the aneurysm so that the aneurysm can be opened and the prosthetic graft of approximately the same size as the aorta is sutured in place. Blood flow is then reestablished through the prosthetic graft. The operation requires a general anesthesia with a breathing tube, extensive intensive care unit monitoring in the immediate post-operative period along with blood transfusions and stomach and bladder tubes. All of this imposes stress on the cardiovascular system. This is a high-risk surgical procedure with well-recognized morbidity and mortality.
More recently, significantly less invasive clinical approaches to aneurysm repair known as endovascular grafting have been proposed. (See, Parodi, J. C., et al. xe2x80x9cTransfemoral Intraluminal Graft Implantation for Abdominal Aortic Aneurysms,xe2x80x9d 5 Annals of Vascular Surgery, 491 (1991)). Endovascular grafting involves the transluminal placement of a prosthetic arterial graft in the endoluminal position (within the lumen of the artery). By this method, the graft is attached to the internal surface of an arterial wall by means of attachment devices such as expandable stents, one above the aneurysm and a second below the aneurysm.
Although endovascular grafting represents a desirable improvement over traditional surgical repair, current endovascular graft systems suffer from certain deficiencies. For example, current endovascular graft systems typically are unsuitable for use in an aneurysm which is tortuous. Aneurysms in the aorta create tortuosity as they grow. Aneurysms grow both in diameter and length, thus xe2x80x9cpushingxe2x80x9d the adjacent upper and lower portions of the arteries upward and downward, respectively. Since the aorta is relatively xe2x80x9cfixedxe2x80x9d at the renal arteries, the portion of the aorta below and near the renal arteries becomes bent and curved in order to accommodate the added length. A similar phenomenon occurs below the aneurysm in the iliac arteries, leading to tortuous iliacs. As many as 20% of aortic aneurysms may have so much tortuosity that they are unable to be fitted with an endovascular graft of this kind. Such systems are unable to conform to the curved walls of the vasculature due to the tortuosity caused by the growing aneurysm.
A specific problem is the xe2x80x9cangulationxe2x80x9d or bend in the neck of the aorta, where it meets the upper part of the aneurysm. This angulation may result in several problems which limit the effectiveness of traditional endovascular graft systems which do not have designs that conform to the tortuosity and angulation above the aneurysm. First, since these systems are typically anchored above the aneurysm with a stent, a portion of the stent may extend into the blood flow path, creating turbulence which may result in blood clotting. It is well-known that in coronary vessels, stents used to treat constrictive lesions must be well apposed to the wall of the vessel to prevent the possibility of thrombosis. Second, a non-conforming upper stent will not place the upper end of the graft in good apposition to the aortic wall, making it difficult to obtain a good seal with a conventional endovascular graft system. Such is illustrated in FIG. 2, showing a generic endovascular graft attached to a conventional non-conforming expanded metal stent in the neck of a tortuous aortic neck. Since this conventional stent will not conform to the tortuosity of the aorta, an upper edge 1 of the stent extends into the blood flow path increasing the chance of thrombosis. Further, a lower edge 2 is not apposed to the wall of the aorta so that the graft material 3 affixed to it does not properly seal. A third problem with non-conforming attachment systems is that once placed in tortuous or angulated aneurysmal anatomy, they are unstable and can xe2x80x9cpop-outxe2x80x9d of position. The attachment system shown in FIG. 2 is an example of an unstable attachment system. Conventional endovascular graft systems having an attachment system intended to project across and above the renal artery ostia also pose a different problem since the attachment system obstructs the renal arteries making it difficult, if not impossible, to effect a repair on a renal artery once the stent is in place.
Thus, a need exists for a prosthetic endovascular graft system which will permit stable conformance to bends within an aneurysm, while providing a good seal to the vasculature.
Another challenge for endovascular grafting of aortic aneurysms relates to the need for graft systems to be delivered in as small of a xe2x80x9cprofilexe2x80x9d as possible. This has driven the design of most endovascular grafting systems to be fabricated with very thin-walled graft conduits. This thin walled conduit, usually coupled to an internal support framework, typically a metallic framework attached to the graft conduit on either the inside or on the outside, is susceptible to xe2x80x9cwear and tearxe2x80x9d mechanisms arising from the pulsatile blood pressure and flow in the aorta. Numerous incidences have been reported in the literature of holes and tears being created in the graft conduit from the cyclic, localized rubbing of the metallic framework against the thin walled graft conduits of a variety of endovascular grafting systems.
Thus, a need exists for a prosthetic endovascular graft system which will minimize or eliminate the wearing mechanisms on the tubular graft conduit, enabling the graft system to be safely utilized in patients for long periods of time, i.e. several years, without concern of premature failure due to wear.
Yet another concern of current endovascular graft systems relates more specifically to the long-term integrity of metallic stents which are used for supporting the structure of the graft material. Since portions of many of the stents used for graft support are in direct interface with the aorta (and iliac arteries in the case of biluminal endovascular graft systems), the pulsatile forces that cause pulsatile diameter changes on these vessels are transferred to these stent portions. This pulsation in the stents leads to cyclic stressing, and can cause premature fatigue failure and breakage.
Thus, a need exists for a prosthetic endovascular graft system which incorporates stents that are designed to minimize cyclic stresses and thus avoid fatigue failure.
This invention is an endovascular graft system for use in repairing aneurysms. In one aspect, the invention is an endovascular graft system capable of being deployed at a desired location within a vessel. The graft system includes an aortic stent having first and second ends, a trunk formed of a graft material having an interior surface defining a lumen and being affixed to the second end of the aortic stent, and a plurality of stents affixed to and supporting the interior surface of the trunk, the plurality of stents being spaced apart such that fully unsupported regions of the trunk lie between adjacent stents. The graft material of the trunk is affixed to the aortic stent and to the plurality of stents in a manner which limits movement of the graft material with respect to the aortic stent and the plurality of stents. The graft material of the trunk may be crimped toward the lumen in the unsupported regions between stents. The trunk has first and second branches configured such that the lumen comprises a main lumen and first and second branch lumens and wherein the plurality of stents includes a first or mid-stent located in the main lumen between the aortic stent and the first and second branch lumens and further includes a plurality of second stents located in the first and second lumens.
In another aspect, this invention is a stent for placement in a vessel of a patient""s vascular system. The stent comprises a substantially tubular body portion having a plurality of struts, each strut having first and second ends and a midpoint located midway therebetween, each end of the plurality of struts intersecting with an end of at least one adjacent strut to form a plurality of strut intersections, at least one strut being configured to taper between the midpoint and the first and second ends in a manner that is gradual and substantially continuous. The stent has a tubular body portion which defines a longitudinal axis and has a first end and a second end. A plurality of intersecting struts adjacent the first end form a substantially diamond shape pattern at the first end of the stent and a plurality of intersecting struts adjacent the second end form a substantially zigzagged pattern at the second end of the stent. The diamond shaped pattern and zigzagged pattern are connected by a plurality of longitudinal struts which are parallel to the longitudinal axis of the stent. The strut which is configured to taper may be one or all of the struts which are adjacent the first end of the stent. The tapering strut may be configured such that the strut tapers from a larger dimension at the midpoint to smaller dimensions at the first and second ends or from a small dimension at the midpoint to larger dimensions at the first and second ends.
In another aspect the invention is a delivery catheter for delivering and deploying an endovascular graft system at a desired location within a vessel of a patient""s vascular system. The catheter includes a handle and a shaft having a distal end and a proximal end, the proximal end being connected to the handle, the shaft further having an outer surface and defining an inflation lumen and a guidewire lumen. A balloon is attached at a location spaced from the distal end of the catheter. The balloon has an interior in fluid communication with the inflation lumen. A transition element is affixed to the balloon. The transition element has a distal portion between the balloon and the distal end of the catheter, the distal portion being configured to provide increasing stiffness from the distal end of the catheter to the balloon. The shaft, balloon and transition element together form a portion of an inner catheter. An outer sheath defines a lumen which contains the inner catheter. The outer sheath is configured to move from an unretracted position to a retracted position and has a distal end positioned about the balloon when in the unretracted position. The distal portion of the transition element may taper outwardly from the distal end of the catheter to the balloon. The lumen of the outer sheath has a first diameter at the distal end of the outer sheath which is less than the diameter of the balloon when inflated.
In another aspect, the invention is a delivery catheter for delivering an endovascular graft system at a desired location within a vessel of a patient""s vascular system. The delivery catheter includes a shaft. First and second graft components are positioned about the shaft, the first graft component being positioned distally of the second graft component. The first graft component is configured to be deployed in the vessel prior to deployment of the second graft component. Both the first and second graft components have proximal and distal portions, the distal portion of the second graft component being configured to be deployed within the proximal portion of the first graft component. The catheter has a retractable sheath which defines a lumen containing the shaft and the first and second graft components. The sheath is configured to deploy the first graft component when it is withdrawn a first distance and to deploy the second graft component when it is withdrawn a second distance. Means are included for stabilizing the position of the distal portion of the second graft component with respect to the proximal portion of the first graft component when the sheath is being withdrawn the second distance.
In a further aspect the invention is a delivery catheter for delivering an endovascular graft system at a desired location within a vessel of a patient""s vascular system. The delivery catheter includes a handle and a shaft connected to the handle. First and second graft components are positioned about the shaft, the first graft component being positioned distally of the second graft component. The first graft component is configured to be deployed in the vessel prior to deployment of the second graft component. The first and second graft components each have proximal and distal portions, the distal portion of the second graft component being configured to be deployed within the proximal portion of the first graft component. The distal portion of the second graft component has a fastening element. A retractable sheath defines a lumen which contains the shaft and the first and second graft components. The handle is configured to retract the sheath to deploy the first graft component when the sheath is retracted a first distance and to deploy the second graft component when the sheath is retracted a second distance. A stabilizing element connected at one end to the handle and at another end to the fastening element of the second graft component stabilizes the second graft component with respect to the first graft component during deployment. The handle, stabilizing element and fastening element are configured such that the stabilizing element is retracted in a manner that disconnects the stabilizing element from the fastening element when the second graft component is deployed. The second graft component includes a stent located at the distal portion which has an eyelet comprising the fastening element. The stabilizing element may be a wire.